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oeyhaga

Three lead screws and one nema 17 motor remix for C/D/J-bot

by oeyhaga Mar 18, 2017
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Hi , I was thinking about a solution with three lead screw single motor and pillow block when I saw your solution ready made :)
Are you sill happy with this solution?
I saw you are using 2040 Vslot on the lowest X frame Have you had rigidity issue?
Can you tell me the clearance from the floor of your printer? It seems raised compared to the original d-bot and I am worried about not having enough space to fit the motor.
Can you tell me the measure of your belt?
Last question I saw you connected the T8 bar with 2 pillow holder , one at the base and one at the top of the frame. Isn't it over constrained?
I was thinking about using only one pillow holder at the base

Question about your leadscrews. If you start with a small pulley on the motor, and move to a bigger pulley on the leadscrews, how does that effect your steps per mm? I'm assuming it's just a normal ratio? Like if there's a 20 tooth pulley on the motor, and a 60 tooth pulley on the leadscrew, would I need to triple the steps per mm that I would have with a normal leadscrew/motor set up?

Also, I'm not an engineer, but would this add extra torque to the system since it's acting like a gear reducer? My printer is pretty big, and the bed is a thick piece of aluminum to prevent sagging that you'd see on a print surface this big. I'm using 4 lead screws, one in each corner, and I belted two together on each side, and each side has an independent Z endstop. But with my current set up I'm getting a lot of binding and resistance which is causing the motor to slip and skip steps.

This system looks like it should function better, plus with the different size pulleys I'll get more torque thanks to the gear reduction. Am I talking crazy or does this make sense?

Hi. Nice printer. :)

I think using three screw is better then 4 to avoid binding.
Your theory with the steps per mm is correct. (https://www.prusaprinters.org/calculator/#stepspermmlead)
When I use the bigger pulleys, I can move heavyer loads with my steppers. :)

Im no expert, and far from an engineer :)

are those pillow blocks setup with thrust bearings? like, designed for vertical loads instead of radial loads like normal bearings?

Do you have an STL for the z motor mount you are using? It doesnt look like the normal one and my search skills are failing me.

Oeyhaga; I'm designing a derivative of your design, with 2 leadscrews at the front, resting on KFL-08 mounts, directly attached to the extrusions, and 1 leadscrew at the rear. I've sourced all my parts and I'm printing components now ... cutting extrusions this week. The following is a link to my design though, as a WIP not a lot is up. http://www.thingiverse.com/thing:2386365

There is 2 renders which demonstrate the way I think I am going to get this to work.

I personally think I've come up with a reasonable arrangement, which allows for a large amount of teeth to be engaged on each pulley, and the ability to use the H bar to tension the belt.

I'd love some feedback from you, on whether you think this design will work.

M-Bot, 400x300x400mm Build Volume, 3 leadscrews, Titan Aero direct drive, IR-bed leveling

Looks really good. I would add a method of tighting the belts. Maybe mounting the motor to the center extrusion? If it works well, it makes the jbot design unnessessary :)

Ahh, so J-bot is the 4 wheel guides? I'll keep you posted on how it goes. With any luck this is a good solution.

Figured out that the belt is on the wrong side of the motor-pulley. Will be correcting that.

Looks okey for me..?

Ah yeah, I had a different render up there. Originally put the motor on the centre extrusion, then realised I couldn't get a belt that long. Now I've arranged it so the motor is back in the centre as you suggest, with enough room, and the belt on the correct side. Should be able to use that to tension it.

Do you think that running the 2 leadscrews on the opposite side to the wheels will help prevent wobble?

I think is worth the try. Without the jbot front braze you might get some side to side wobble,but if it works you would save money. Easy enough to add brace later if it does not work. Another way to tenshioning the belts are with pins with pulleys on like in my design. Looking forward to you testing it.

I've attached the leadscrews, and there seems to be no play. My wheel mounts are rock-solid 3 wheel types, also linked as a source for my remix, though I modified them a bit for my available hardware. The bed assembly is easy to move by turning each leadscrew, but basically impossible to shift by rocking it.

Nice job! ☺️☺️

What are the lengths of your lead screws?

600mm. My dbot is not stock size.

Hi buddy,

I'm about to embard on my D-Bot build and am absolutely gonna put this design to use. Thank-you for sharing!

I was wondering, I have seen some people replace the wheeled runners with smooth rods, citing that this makes the platform more stable. Would you reccomend this or would the three wheeled carriage replacement be enough?

Cheers! :)

Hi,

Im very happy with my wheel solution on z-axis. Im using 3-wheeled Z guide (http://www.thingiverse.com/thing:1802733) on all four corners like on the J-bot (http://www.thingiverse.com/thing:1721957). Have never compared it to smooth rods, so hard to say if its better/worse/same. Would think you needed thicker then 8mm rods, and get them sent to you without bending them :) But whatever solution I think using three rods really makes the bed rock solid.

3-wheeled Z guide (Re-D-Bot)
J-Bot Core-XY?

Awesome! Thanks for getting back to me.
I've decided to go with the tried and tested 3 wheeled guides!

Possibly being a bit dense now, the rods I bought came with some brass threaded rod nuts. Are the anti backlash nuts necessary? £15 each seems steep? If I do not use the anti backlash nuts will I still need to use the modded bracket?

Regards!

Dont know. The brass nuts is used in the stock dbot build, but never tried it.

Hi.
I got my pulleys from random seller on ebay.

On the rods I have a GT2 Timing Pulley 40 teeth with 8mm bore and 6mm belt width.
Like this one:
http://www.ebay.com/itm/GT2-Timing-Pulley-40-teeth-8mm-bore-/331664576496?hash=item4d38bfcff0:g:1SUAAOSwgQ9Vpxik

For the motor I have a GT2 Timing Pulley 20 teeth 5mm bore 6mm belt width.
Like this one:
http://www.ebay.com/itm/GT2-6mm-Timing-Pulley-20-teeth-Alumium-Bore-5mm-RepRap-CNC-3D-Printer-Prusa-/172367625697?hash=item2821e93de1:g:808AAOSw-CpX-CjN

How do you resolve differential tension in the belt between the pulleys?

Did'nt think of that. Did'nt seem to be a problem. The belt is a bit tigher around the motor mount. I have now add a single pin with a bearings between two of the rods to add tension. A pin is easly made with a M5 screw with a tnut on buttom and two nuts and and two Flange Ball Bearing on top. Iv added some photo. Seems tight all over now. Thanks for the tip :)

I only ask as I have a 2-motor linked with a belt setup on my C/D-bot and while it does improve the misalignment compared to a standard independent 2-motor setup, it doesn't solve it entirely. Mine has been running 24/7 for around 6 months and its only just developed a slight misalignment in belt tension.